1. Field of the Invention
The present invention relates in general to safety mechanisms for elevator car doors and in particular to a locking mechanism for preventing the opening of an elevator car door when the car is situated between floor landings in an elevator shaft.
Elevator cars are customarily provided with horizontally movable car doors consisting of two sections. The sections either part in the center or slide together to one side to allow entrance into the car. For most elevators, it is required that the car doors be locked by mechanical or electrical means when the car is not positioned within a predetermined landing zone such that the door cannot be manually opened from within the car. For example, the ANSI/ASME Code Rule 110.6 requires that passenger elevator hoistway doors be so arranged that they may be opened by hand from within the elevator car only when the car is within the landing zone, except at an entrance which has been locked out of service.
Generally, the sections of the elevator car door cooperate with respective floor landing door sections when the car is within the landing zone to disengage a locking mechanism, thereby allowing the doors to open. In the usual instance, an interlocking means is provided on the opposing faces of the car and landing doors to release the locking mechanism when the car is properly positioned.
2. Description of the Prior Art
U.S. Pat. No. 1,838,524 to Brown discloses a safety device for an elevator system employing horizontally-sliding car and hatchway floor doors. The safety device includes a channel strip mounted on the car door and a plurality of rail sections mounted on the hoistway doors and the shaft walls. When the car floor and the landing floor are in substantial alignment, the channel strip engages the rail section on the hoistway door for simultaneous opening movement. As the car moves away from the floor, the channel strip engages a rail section on the shaft wall, thereby preventing opening of the car door.
U.S. Pat. No. 2,499,979 to Smith discloses an operating mechanism for the landing doors of elevators. A cam plate must be engaged with a roller on a lock bar to unlock the door. Such unlocking can occur only if the car is located in front of the landing in the proper position for unloading or loading when the operator starts the operation of the door mechanism.
U.S. Pat. No. 3,991,858 to Westerlund discloses a locking device for a holding door on an elevator shaft. The locking device includes a barrier member that is interconnected to a locking arm. The locking arm is alternately engageable and disengageable with a stop means such that the barrier member can be moved out of the way of a holding door when the elevator is adjacent to the holding door.